The Norwegian military has admitted to being hit by a potentially serious targeted cyberattack attack in March, sources in the country have reported.

The attack happened on 25 March when 100 senior military personnel received an email and attachment in Norwegian language which appeared to have come from a government agency in the country.

At least one person opened the attachment, launching malware of an unknown type that compromised the machine before it was stopped from spreading further. The attack was a failure and no data was lost, Major General Roar Sundseth told a Norwegian news site.

“The defence systems are attacked daily, but it’s not often we see such a comprehensive attempt at infiltration as this was. The trend is increasing, though, and the attackers are more goal-oriented,” he said.

Some have speculated that the attack might be connected to the country’s decision to participate in the NATO-led air campaign against Libya, agreed shortly before the 25 March attack, but this only one theory. Countries come under cyberattack at all times, including many with no direct involvement in contentious events.

The country reported an increase in attacks on its companies last summer and was also affected by the Stuxnet worm widely claimed to have been aimed at Iran.